1. Field of the Invention
This invention relates generally to fabrication of semiconductor devices and more particularly to the fabrication of semiconductor devices and more particularly to fabrication of a shallow trench isolation which is not susceptable to buried contact trench formation.
2. Description of the Prior Art
As device dimensions and die sizes continue to decrease to aceive higher density integrated circuits, there is a growing demand for more effective isolation technology. Shallow trench isolation (STI) technology has become more widely used due to the lack of encroachment like the "bird beak" in LOCOS technology and due to the lower susceptability to "Latch-up." However, several problems exist with conventional shallow trench isolation technology. If misalignment occurs during the contact etching process, a trench can form in the buried contact. This trench, known as a buried contact trench creates a leakage path between the contact and the substrate.
Another problem associated with shallow trench isolation technology is called the "kink effect" caused by oxide thinning. During conventional STI etch, a recess is formed near the edge of the STI. This geometry causes the gate oxide to be thinner over the edge formed where the recess begins, resulting in a reduced threshhold voltage and additional standby current.
Recent research has shown several advantages to nitrogen implantation into silicon dioxide isolations. For example, Formation of Ultrathin Nitrided SiO2 Oxides by direct Nitrogen Implantation into Silicon, Journal of Electrochemical Society, Vol. 142 No. 8, August 1995, discloses a process for silicon dioxide nitridation to improve resistance to the hot carrier effect while minimizing ion implantation damage. Another article, High Performance 0.2 .mu.m CMOS with 25 .ANG. Gate Oxide Grown on Nitrogen Implanted Si Substrates, IEDM 96-499, discloses that implanted nitrogen can prevent Boron penetration and supress short-channel effect and drain induced barrier lowering (DIBL) effect.
The importance of overcoming the various deficiencies noted above is evidenced by the extensive technological development directed to the subject, as documented by the relevant patent and technical literature. The closest and apparently more relevant technical developments in the patent literature can be gleaned by considering the following patents.
U.S. Pat. No. 5,316,965 (Philipossian et al.) shows a nitrogen ion implantation to acheive a comparable etch rate to a thermal oxide pad layer.
U.S. Pat. No. 5,468,657 (Hsu) discloses a SIMOX process with N.sub.2 ion implant into the oxide.
U.S. Pat. No. 5,516,707 (Loh et al.) shows an angled nitrogen implantation into source/drain regions to improve hot carrier immunity.
U.S. Pat. No. 5,741,740 (Jang et al.) shows a method of filling a trench which may include nitrogen treatment of a liner oxide prior to filling the trench.
U.S. Pat. No. 5,763,315 (Benedict et al.) shows an oxynitride liner formation prior to filling a trench.